1. Field of the Invention
The present invention relates to a package for hermetically packaging an electric device such as a resonator and a hybrid IC. More particularly, it relates to a package suitable for packaging a quartz device such as a quartz crystal resonator, a quartz filter, and a quartz surface acoustic wave filter used in circuits for mobile wireless communication equipment such as portable telephones.
2. Description of the Related Art
Recently, as mobile wireless communication equipment such as portable telephones have become widely used, there has been an increasing demand for a quartz device for a reference frequency source and a filter used in such equipment.
Hereinafter, a conventional ceramic package, a quartz crystal resonator, a quartz filter, and a quartz surface acoustic wave filter will be described referring to FIGS. 30 to 33.
FIG. 33 shows an exemplary structure for the conventional ceramic package. In FIG. 33, the conventional ceramic package includes a ceramic covering member 3701 and a ceramic body member 3702. On the top face of the ceramic body member 3702, a packaging glass 3702a is formed using a paste containing glass powders. A recessed portion 3702b is formed at the ceramic body member 3702.
As for the package shown in FIG. 33, a packaging operation is performed as follows: an object to be packaged is first put into the recessed portion 3702b, the ceramic covering member 3701 is overlaid thereon, and finally the container is wholly heated up to a temperature at which the glass 3702a melts. Such a packaging operation is described, for example, in Nikkei Electronics, Jan. 7, 1991 (No. 517), pp. 167.
FIG. 30 shows an exemplary structure for the conventional quartz crystal resonator. In FIG. 30, the conventional resonator includes a quartz plate 3401, an electrode 3402, conductive adhesives 3403 and 3404, supporting members 3405 and 3406, leading members 3407 and 3408, a supporting plate 3409, and a cap 3410. The electrode 3402 is formed on each face of the quartz plate 3401. The quartz plate 3401 functions as an electric resonator, whose resonance frequencies are determined by the thickness and the elastic constant thereof. The quartz plate 3401 is connected to the supporting members 3405 and 3406 both supported by the supporting plate 3409 by means of the conductive adhesives 3403 and 3404, and thus the quartz plate 3401 is electrically connected to the supporting members 3405 and 3406. In addition, the quartz plate 3401 is electrically connected to the outside via the leading members 3407 and 3408 via the supporting members 3405 and 3406. Furthermore, the cap 3410 packages the quartz plate 3401. The packaging operation is generally performed using a solder welding method.
FIG. 31a is a front view showing a structure for the conventional quartz filter, while FIG. 3lb is a back view showing the structure for the conventional quartz filter. In FIGS. 31a and 31b, the conventional quartz filter includes a quartz plate 3501, electrodes 3502 to 3505, conductive adhesives 3506 to 3509, supporting members 3510 and 3511, leading members 3512 to 3515, a supporting plate 3516, and a covering member 3517. The electrodes 3502 and 3504 are disposed so as to be opposed to the electrodes 3503 and 3505, respectively.
The electrode 3502 is led to the outside by the leading member 3512 via the conductive adhesive 3506 and the supporting member 3510. The electrode 3504 is led to the outside by the leading member 3514 via the conductive adhesive 3508 and the supporting member 3511. Similarly, the electrode 3503 is led to the outside by the leading member 3513 via the conductive adhesive 3507. Likewise, the electrode 3505 is led to the outside by the leading member 3515 via the conductive adhesive 3509. The electrodes 3503 and 3505 are generally earthed.
Upon inputting an electrical signal to the electrode 3502, the quartz plate 3501 resonates at frequencies determined by the thickness and the elastic constant thereof. The thus caused resonance is mechanically propagated in the quartz plate 3501, so that an electrical field is generated between the two electrodes 3504 and 3505, and consequently the electrical signal can be picked up from the electrode 3504. That is, the quartz filter can function as a band-pass filter for the frequencies which are determined by the thickness and the elastic constant of the quartz plate 3501. In addition, the quartz plate 3401 is sealed by the supporting plate 3516 and the covering member 3517. Such a packaging operation is generally performed using the solder welding method.
FIG. 32 shows a structure for the conventional surface acoustic wave filter. In FIG. 32, the conventional surface acoustic wave filter includes a piezoelectric substrate 3601, a covering member 3602, a base member 3603, an interdigital transducer (IDT) type electrode 3604, a bonding pad 3605, and glass 3606. As shown in FIG. 32, the IDT type electrode 3604 is formed on the piezoelectric substrate 3601. Upon inputting an electrical signal to the electrode 3604, surface acoustic waves are excited on the piezoelectric substrate 3601, and finally only waves having certain frequencies can be propagated. Herein, an electrode pattern of the IDT type electrode 3604 and an effective piezoelectric constant of the piezoelectric substrate 3601 determine which surface acoustic waves can be propagated. According to such principles, a surface acoustic wave filter having the desired filter characteristics can be obtained by appropriately selecting the electrode pattern of the IDT type electrode 3604, and the material for and the cutting angle of the piezoelectric substrate 3601. The packaging is performed as follows: First, the piezoelectric substrate 3601 is fixed onto a recessed portion of the base member 3603 by using an adhesive. Thereafter, the glass 3606 is applied to the base member 3603, and the covering member 3602 is overlaid thereon. Finally, the container is wholly heated up to a temperature at which the glass 3606 melts, thereby integrating the covering member 3602 with the base member 3603.
The above-mentioned surface acoustic wave filter and package have some problems. For example, according to the conventional glass packaging method, a glass paste is used for packaging, so that gas is disadvantageously generated from the glass paste. As a result, the device characteristics are likely to deteriorate due to age. In addition, the use of glass as the adhesive necessitates the need for additional space for melted glass to flow for the packaging portion, which makes it difficult to miniaturize the device. Furthermore, such a complicated manufacturing process leads to a high production cost. Moreover, the solder welding method has a problem in that the height of the package is made higher as shown in FIGS. 30 and 31, which makes the face mounting of the package inappropriate.
In addition, not only for the structural reason, the above-mentioned quartz crystal resonator and quartz filter cannot be readily made compact because many components such as the supporting members, leading members, supporting plates, and covering members should be included therein. Moreover, the use of the conductive adhesive for the bonding of each component generates gas, and consequently the package is likely to deteriorate due to age.